The present invention involves a device for unlocking a compartment of an opening mechanism, and in particular, of a thermal printing mechanism, the unlocking device being designed to make it easier to load and unload the paper used in a thermal printing device of this type.
The printing mechanisms are generally made up of a printing head affixed to a frame. The thermal printing head comprises a ceramic support that carries the line of heating points and silicon chips or integrated circuits for controlling their supply. The printing head can pivot relative to the frame, most generally along an axis parallel to a longitudinal side of the frame. A roller is united as a single piece with the frame in a manner so that its longitudinal axis is also parallel to it on a longitudinal side of the frame. The printing head is held by a spring supported on the roller. The position of the roller must thus be perfectly controlled in order to obtain a perfect alignment with the thermal printing head. The printing medium usually consists of a roll of paper whose one side is sensitive to heat. This printing roller is driven in rotation by means of a drive cylinder, also called a drive capstan, which itself is activated by a system of pinions and by a small electric motor.
In the case of opening mechanisms for thermal printing devices, the compartment designed to accommodate the roll of paper is closed by a cover that is made of one or more articulated parts, whereby the cover supports the printing roller and makes it possible to bring the printing roller into contact with the chassis.
The locking of the roller onto the printing head is done by a spring united with the chassis that brings the roller into contact with the printing head and between which, the paper to be printed becomes inserted.
The pressure of the printing head on the roller enables the system to be locked in a closed position, either by a condition on the respective positions of the axis of rotation of the cover and the support direction of the printing head, or by a condition on the shape of the spring or on the shape of the chassis.
In order to be reliable, the known locking systems require a large enough pressure of the printing head on the roller in order to ensure a correct alignment between the printing head and the roller, and in order to not be able to open very easily, for example, during a drop or a jolt or when tension is exerted on the paper.
The fact of exerting such pressure in order to ensure closing, this pressure being exerted against a relatively sizeable resistance, does not generally pose a problem to the user, since it is always sufficient to press on the cover to close it. On the other hand, it happens that the force to be exerted in order to open the cover is also relatively sizeable. The action for opening the cover consists in pulling on the cover at the positions provided with grooves for this purpose. The sizeable force to be exerted can thus result in a sudden uncoupling of the cover, which can result in its breaking. On the other hand, these mechanisms are generally of a small size, in a manner such that the user is not very inclined to exert a sizeable pulling force on these mechanisms, which poses an ergonomic problem. Moreover, if the user does not pull on the cover in the direction that is absolutely perpendicular to its axis of rotation, the cover will twist or break, so that the printing device itself can no longer function correctly.
The present invention applies in this context and its purpose is to propose a thermal printing device in which the cover of the compartment intended to receive the paper roll can be maneuvered in the opening direction as in the closing direction in a simple manner and without making sizeable forces necessary, whereby the opening and closing mechanism only has to consist of a reduced number of parts so as not to have a negative influence on the cost of such a printing device and on its reliability.
For this purpose, the present invention has as its object a device for unlocking a compartment of an opening mechanism, in particular, a thermal printing mechanism, comprising a chassis, the compartment being designed to receive a paper roll, and being closed by a cover.
According to the present invention, a lever is mounted to rotate on the cover and comprises a maneuvering part, whereby the lever consists of stops able to act together with the sides of the chassis in order to cause the rotation of the cover relative to the chassis when the lever is rotated relative to the cover.
According to a characteristic of the present invention, the maneuvering part of the lever is housed in an opening of the cover.
Preferably, the opening is formed on the median part of its main side and receptacles are formed on the portions that extend perpendicularly to the main side of the cover.
According to a characteristic of the invention, the receptacles are formed between the openings designed to act together with pins united with the chassis and allowing the cover to rotate relative to the chassis and with slots designed to receive the ends of the axle of a support and drive roller for paper delivered from the paper roll.
In an advantageous manner, the lever comprises a maneuvering part, having a shape that is approximately complementary to that of the opening of the cover, and it is equipped with extensions carrying at their free ends, rotating axes intended to come to engage in the receptacles formed in the cover, and stops intended to act together with the sides of the chassis.